/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.solr.schema;

import org.apache.lucene.search.SortField;
import org.apache.lucene.document.Fieldable;
import org.apache.solr.search.function.ValueSource;
import org.apache.solr.search.function.FileFloatSource;
import org.apache.solr.search.QParser;
import org.apache.solr.response.TextResponseWriter;
import org.apache.solr.response.XMLWriter;
import org.apache.solr.common.SolrException;

import java.util.Map;
import java.io.IOException;

/**
 * Get values from an external file instead of the index.
 * 
 * <p/>
 * <code>keyField</code> will normally be the unique key field, but it doesn't
 * have to be.
 * <ul>
 * <li>It's OK to have a keyField value that can't be found in the index</li>
 * <li>It's OK to have some documents without a keyField in the file (defVal is
 * used as the default)</li>
 * <li>It's OK for a keyField value to point to multiple documents (no
 * uniqueness requirement)</li>
 * </ul>
 * <code>valType</code> is a reference to another fieldType to define the value
 * type of this field (must currently be TrieFloatField or FloatField
 * (valType="pfloat|float|tfloat") if used). This parameter has never been
 * implemented. As of Solr 3.6/4.0 it is optional and can be omitted.
 * 
 * The format of the external file is simply newline separated
 * keyFieldValue=floatValue. <br/>
 * Example: <br/>
 * <code>doc33=1.414</code> <br/>
 * <code>doc34=3.14159</code> <br/>
 * <code>doc40=42</code>
 * 
 * <p/>
 * Solr looks for the external file in the index directory under the name of
 * external_&lt;fieldname&gt; or external_&lt;fieldname&gt;.*
 * 
 * <p/>
 * If any files of the latter pattern appear, the last (after being sorted by
 * name) will be used and previous versions will be deleted. This is to help
 * support systems where one may not be able to overwrite a file (like Windows,
 * if the file is in use).
 * <p/>
 * If the external file has already been loaded, and it is changed, those
 * changes will not be visible until a commit has been done.
 * <p/>
 * The external file may be sorted or unsorted by the key field, but it will be
 * substantially slower (untested) if it isn't sorted.
 * <p/>
 * Fields of this type may currently only be used as a ValueSource in a
 * FunctionQuery.
 * 
 * @version $Id: ExternalFileField.java 1215504 2011-12-17 14:54:22Z erick $
 */
public class ExternalFileField extends FieldType {
	private FieldType ftype;
	private String keyFieldName;
	private IndexSchema schema;
	private float defVal;

	@Override
	protected void init(IndexSchema schema, Map<String, String> args) {
		restrictProps(SORT_MISSING_FIRST | SORT_MISSING_LAST);
		// valType has never been used for anything except to throw an error, so
		// make it optional since the
		// code (see getValueSource) gives you a FileFloatSource.
		String ftypeS = args.remove("valType");
		if (ftypeS != null) {
			ftype = schema.getFieldTypes().get(ftypeS);
			if (ftype != null && !(ftype instanceof FloatField)
					&& !(ftype instanceof TrieFloatField)) {
				throw new SolrException(
						SolrException.ErrorCode.SERVER_ERROR,
						"Only float and pfloat (Trie|Float)Field are currently supported as external field type.  Got "
								+ ftypeS);
			}
		}
		keyFieldName = args.remove("keyField");
		String defValS = args.remove("defVal");
		defVal = defValS == null ? 0 : Float.parseFloat(defValS);
		this.schema = schema;
	}

	@Override
	public void write(XMLWriter xmlWriter, String name, Fieldable f)
			throws IOException {
		throw new UnsupportedOperationException();
	}

	@Override
	public void write(TextResponseWriter writer, String name, Fieldable f)
			throws IOException {
		throw new UnsupportedOperationException();
	}

	@Override
	public SortField getSortField(SchemaField field, boolean reverse) {
		throw new UnsupportedOperationException();
	}

	@Override
	public ValueSource getValueSource(SchemaField field, QParser parser) {
		// default key field to unique key
		SchemaField keyField = keyFieldName == null ? schema
				.getUniqueKeyField() : schema.getField(keyFieldName);
		return new FileFloatSource(field, keyField, defVal, parser);
	}

}
